In many industrialized processes, heat is required at a temperature which is readily supplied by a circulating liquid, such as water. Such circulating streams require heating at a heat source to reheat the circulating liquid stream after it has given up heat in the area in which the heat was desired.
As indicated previously, one area wherein frequent applications of this type arise is in the revaporization of LNG.
In many remote areas of the world large natural gas deposits are found. These natural gas deposits, while constituting a valuable resource, have little value in the remote areas in which they are located. To utilize these resources effectively the natural gas must be moved to a commercial market area. This is frequently accomplished by liquefying the natural gas to produce LNG, which is then transported by ship or the like to a market place. Once the LNG arrives at the market place, the LNG must be revaporized for use as a fuel, for delivery to pipelines and the like. Other cryogenic fluids frequently require revaporization after transportation also, but by far the largest demand for processes of this type is for cryogenic natural gas revaporization.
The revaporization of the cryogenic natural gas requires the input of substantial quantities of heat. While seawater has been used in areas where seawater is readily available, certain disadvantages attend the use of seawater, not the least of which is lack of availability in some areas in which the LNG is to be revaporized. Other disadvantages relate to the corrosion of heat exchange surfaces by the seawater and the like.
In some instances, air has been used as a heat exchange medium to revaporize the cryogenic natural gas. One such process is shown in U.S. Ser. No. 11/133,762 entitled “Air Vaporizer” filed May 19, 2005 by Martin J. Rosetta, et al. This application is hereby incorporated in its entirety by reference. Other systems may also be used for the revaporization of the cryogenic liquid and include indirect heat exchangers such as shell and tube heat exchangers, direct fired heat exchangers in indirect heat exchange contact with the cryogenic gas and the like. In all such cases, substantial heat is required to revaporize the cryogenic natural gas.
In the air vaporization processes particularly, it would be desirable if a recirculating liquid stream could be used to heat the air prior to or during its passage through the revaporization vessels. Further it is desirable to heat the vaporized gas with a warm or hot liquid solution to raise it to a pipeline temperature after vaporization.
A continuing effort has been directed to the development of efficient equipment to provide a heated hot liquid stream in a recirculating loop for use in such processes.